The present invention relates to a zipper that has been molded of plastic and is used for closing the mouth of a bag.
Such a zipper made of resin may be made with a structure where it is to be nipped, for its attachment, into the portion corresponding to the mouth of bag during bag-making and during automatic packing.
In this attachment, both the elements (bag and zipper) can be attached through their fusion by a heat sealing method if the bag side and the zipper side possesses the property allowing heat fusion.
However, if both the elements do not exhibit such a heat fusion property, a film having the heat fusion property with the bag side is pasted up to the outside of zipper tape, or a film having the heat fusion property with the zipper tape is pasted up to the bag side. Or, if this type of structure is not adopted, a bonding agent is coated to the adhesive face on each of such occasions for pasting them up to each other.
However, the attachment method of the zipper involves problems as follows.
a. The zipper tape needs to have the thickness of at least some 150.mu. in order to prevent its melting during the fusion step.
b. In the event that the heat fusion film is to be pasted up to the outside of zipper tape, its thickness is increased by this film portion.
c. Because the thickness of zipper entirety is increased by such items "a" and "b", the heat sealing property deteriorates in the portion of crossing the zipper when side-sealing the bag, which becomes the cause for pin holes.
d. The pasting method with use of the bonding agent is complex in the process and at the same time is difficult with respect to quality control.